Silane coupling agents are compounds having in their molecule an organic functional group and a hydrolizable group reactive with inorganic materials. Since the silane coupling agents are, due to their functional groups, capable of chemically bonding an organic polymer with an inorganic material, such as silica, thereby remarkably increasing the mechanical strength of the organic polymer, they are now indispensable in the development of ultrafashionable composite materials.
Aminopropyl silanes such as gamma-aminopropyl alkoxy silanes are used in the art as the silane coupling agent, and it is known that they can be prepared by hydrosilylation of an allylamine, which may be substituted on the nitrogen atom, with a hydrosilane.
For example, Japanese Patent Laid-open Publication No. 60-81189 discloses a process for the preparation of aminopropyl alkoxy silanes, which comprises reacting an allylamine with a hydrosilane using a platinum catalyst, such as chloroplatinic acid, in the presence of a promoter, such as anhydrous sodium carbonate. However, the reaction of an allylamine with a hydrosilane in the presence of a platinum catalyst, such as chloroplatinic acid, inevitably produces the corresponding beta-aminopropyl alkoxy silane, which may be referred to herein as the beta-isomer in addition to the desired gamma-aminopropyl alkoxy silane, which may be referred to herein as the gamma-isomer, normally with a ratio of the gamma-isomer to the beta-isomer of from 4 to 6, posing a problem in that the selectivity of the desired gamma-isomer is not satisfactorily high.
Japanese Patent Laid-open Publication No. 61-229885 discloses a process for the preparation of aminopropyl alkoxy silanes by reacting an allylamine with a hydrosilane in the presence of a catalyst comprising rhodium organic tertiary phosphine complex and optionally triphenylphosphine. By this process gamma-aminopropyl alkoxy silanes can be prepared in a high selectivity. The process is disadvantageous, however, in that a prolonged reaction time is required to achieve a high conversion. Further, an excessive amount of triphenylphosphine must be used to achieve a high selectivity of the gamma-isomer. Additionally, the rhodium compounds are so expensive that the aminopropyl alkoxy silanes cannot be produced on a industrial scale without reusing the rhodium compound recovered from the reaction mixture or decreasing an amount of the rhodium compound used. J. of Organomet. Chem., 149, 29-36 (1978) discloses the hydrosilylation of olefins in the presence of a metallic carbonyl catalyst, such as cobalt-, rhodium-, iridium- and iron-carbonyl compounds and teaches that N, N-dimethylaminopropyl triethoxy silane can be obtained in a high yield from N, N-dimethylallylamine and triethoxy silane. It is also stated in this article that when an olefinic amine, such as allylamine is hydrosilylated, the silylation proceeds preferentially on the amine nitrogen atom. This statement means that hydrosilylation of a N-unsubstituted allylamine with a hydrosilane would be unsuitable for the preparation of the corresponding aminopropyl alkoxy silane.